As conventional optical materials, especially as resin lens materials, diethylene glycol bis(allylcarbonate) (e.g. CR-39 (product name) manufactured by PPG Industries, Inc.) is known. This resin has various characteristics as plastic lens material, such as excellent impact-resistance, light weight, excellent dyeability, and good workability properties such as cuttability and polishability. However, since the refractive index 1.50 of a lens obtained by radically polymerizing diethylene glycol bis(allylcarbonate) is low as compared with that of inorganic glass (e.g. refractive index of white crown glass is 1.523), in order to obtain optical properties comparable to those of a glass lens, it is necessary to increase the center thickness, peripheral thickness and curvature of the lens, which inevitably renders the whole lens bulky. Accordingly, there has been a demand for resin which enables production of lens having a high refractive index.
Further, known as an organic glass having a higher refractive index than that of a lens obtainable by radically polymerizing diethylene glycol bis(allylcarbonate) is a lens obtainable by curing a resin containing allylester compound which has an allylester group at a terminal and has a structure derived from polyvalent carboxylic acid and polyvalent alcohol is known. This lens has a higher refractive index than that of a lens obtained by curing diethylene glycol bis(allylcarbonate) through radical polymerization and can be easily cured by radical polymerization, however, the refractive index of the lens cannot be said to be sufficiently high.
Known as lens which can solve these problems and realize a high refractive index are a thiourethane lens obtained by curing through reaction of an isocyanate compound with a compound having a mercapto group and further a sulfur-containing acrylate lens obtained by curing a sulfur-containing acrylate compound through radically polymerization.
However, although a thiourethane lens has a high refractive index and a high impact resistance, its production process entails various problems such as toxicity of the raw material isocyanate compound, the odor of the raw material thiol compound, the odor in process of cutting the thiourethane lens and low abrasion resistance of thiourethane lens.
The method for curing diethylene glycol bis(allylcarbonate) or a resin containing allylester compound as mentioned above is radical polymerization, which has been conventionally employed as lens forming method since long ago and therefore, the method is easy to perform. On the other hand, the method for producing thiourethane lens includes mixing an isocyanate compound with a compound having a mercapto group and then pouring the mixture into a mold to cure. Since the method used such a two-liquid type resin, the procedures are complicated. Further, the curing proceeds not through radical polymerization but through addition reaction between an isocyanate group and a mercapto group. In the curing process, it is important to control the temperature and humidity of the room where the step of pouring the mixture solution into the mold is conducted and also, the curing step requires high technique.
With respect to sulfur-containing acrylate lens, many of sulfur-containing acrylate compounds have high viscosity, and also its high reactivity leads to low storage stability. Still further, in performing polymerization reaction, temperature must be carefully controlled to prevent runaway reaction.
On the other hand, a cured product which can serve as an optical material, which is obtained by reacting a bifunctional five-membered ring dithiocarbonate with bifunctional diamine, is described in JP-A-H08-302013. However, since the reaction is two-liquid type, the preparation operation is complicated. Moreover, there is a problem in this technique that after the two solutions are mixed together, the reaction gradually proceeds, which leads to low stability and therefore, a novel resin composition which can serve as optical material has been demanded.